Can-Bus Terminal Resistance, Checking

WARNING: This page is about a different car, the 2020 Audi A3, 2019 Audi A3, and 2018 Audi A3. However, it is still accessible from the selected car via links, so may be relevant.

General Description

The Engine/Motor Control Module -J623- communicates with all databus capable control modules via a CAN databus.

These databus capable control modules are connected via two data bus wires which are twisted together (CAN_High and CAN_Low), and exchange information (messages). Missing information on the databus (CAN-bus) is recognized as a malfunction and may be stored by the Engine/Motor Control Module -J623- and the other control modules connected to the CAN-bus.

Trouble-free operation of the CAN-bus requires that it have a terminal resistance. This central terminal resistor is located in the Engine/Motor Control Module -J623-.

Special tools and workshop equipment required

Multimeter.
Wiring Diagram.

Test requirements

Fuses OK.
Battery voltage OK.
Switch OFF all electrical and electronic accessories.
Vehicles with automatic transmission, ensure the selector lever position is in "P".
Vehicles with manual transmission, ensure the shifter lever position is in "N" with the parking brake applied.
Observe all safety precautions: SAFETY PRECAUTIONS .
View clean working conditions: CLEAN WORKING CONDITIONS .

Test Procedure

Step	Procedure	Result / Action to Take
1	PERFORM: Preliminary Check to verify the customers complaint. Refer to PRELIMINARY CHECK . -- Was Complaint verified?	-- YES: GO TO: Step 2 CAN-BUS TERMINAL RESISTANCE, CHECKING - 2 . -- NO: GATHER more information from customer about the complaint.
2	IGNITION: OFF. DISCONNECT: Data Bus On Board Diagnostic Interface -J533- harness connector. The Engine/Motor Control Module -J623- must remain connected for the following step. CHECK: Data Bus On Board Diagnostic Interface -J533- harness connector terminals 6 to 16 for resistance. SPECIFIED VALUE: 60 - 72 Ω (@ approx. 20° C). -- Was Value obtained?	-- YES: CONDITION: May be intermittent. PERFORM: Visual Inspection of wiring and component. CHECK: Wiring for open, high resistance, short or harness connector for damage, corrosion, loose or broken terminals. REPAIR: Faulty wiring or connector. GO TO: Step 4 CAN-BUS TERMINAL RESISTANCE, CHECKING - 4 . -- NO: GO TO: Step 3 CAN-BUS TERMINAL RESISTANCE, CHECKING - 3 .
3	REMOVE: Engine/Motor Control Module - J623-. Refer to appropriate repair information. CHECK: Data Bus On Board Diagnostic Interface -J533- harness connector terminal 6 to the Engine/Motor Control Module - J623- harness connector T91 / 80 for resistance. CHECK: Data Bus On Board Diagnostic Interface -J533- harness connector terminal 16 to the Engine/Motor Control Module - J623- harness connector T91 / 79 for resistance. SPECIFIED VALUE: 0.5 Ω (± 0.3 Ω). -- Were Values obtained?	-- YES: REPLACE: Engine/Motor Control Module -J623-. Refer to appropriate repair information. GO TO: Step 4 CAN-BUS TERMINAL RESISTANCE, CHECKING - 4 . -- NO: PERFORM: Visual Inspection of wiring and component. CHECK: Wiring for open, high resistance, short or harness connector for damage, corrosion, loose or broken terminals. REPAIR: Faulty wiring or connector. GO TO: Step 4 CAN-BUS TERMINAL RESISTANCE, CHECKING - 4 .
4	Final Procedure Perform a road test to verify repair. -- Does the original DTC return?	-- YES: CHECK: Data Bus On Board Diagnostic Interface -J533- harness connector for any damaged, pushed-out pins. REPAIR: As necessary. If all electrical connections are OK: REPLACE: Data Bus On Board Diagnostic Interface -J533-. Refer to appropriate repair information. Clear the DTC's. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY . Repair is complete. Generate Readiness Code. Refer to READINESS CODE . Return vehicle to Customer. -- NO: Perform the diagnostic procedure for any DTC's. If no DTC's return, the repair is complete. Return vehicle to customer.